This invention relates to waterless planographic printing. More particularly, it relates to novel sheet constructions which are capable of being direct imaged and are suitable for use in planographic printing wherein conventional fountain solutions are not necessary.
Conventional lithographic plates generally require a dampening thereof with an aqueous fountain solution to effectively wet the background plate area, after which ink is rolled over the plate. The oily ink selectively wets the oleophilic image areas but is repelled from the dampened background areas.
Recently, planographic printing plates not requiring dampening have been developed. These plates require only an inking system to be operative and inherently contain ink repellent non-imaged or background areas. This relatively new concept has come to be known by the term driography, and plates useful therein have been termed driographic plates. Such a printing plate is disclosed in U.S. Pat. No. 3,511,178.
Such plates generally operate on the principle that the background surface areas inherently having sufficiently low adhesion to driographic printing inks that ink applied to the plate by an inking roller will not split away or transfer from the roller to the plate. A surface exhibiting such characteristics has come to be termed "abhesive".
Present techniques for imaging such driographic printing plates, i.e providing ink-receptive image areas thereon, generally involve selective removal of the abhesive coating, removal of a light-sensitive layer after imagewise exposure thereof to actinic radiation, etc. To my knowledge, there is not commercially available a direct image driographic plate, i.e. one that can be imaged by conventional marking techniques, such as pen, pencil or office duplicating machines. In U.S. Pat. No. 3,859,090 there is disclosed a driographic printing plate asserted to be directly imageable by toner powder in an electrographic imaging process. However, the abhesive composition therein requires utilization of a fluorinated or polysiloxane oil, i.e. a liquid, to obtain adequate ink repellency in the background or non-image areas of the plate. Such oils will typically cause blinding of the plate, i.e. the image areas will also tend to repel ink during continued press operation by wetting of the total plate surface by the oils due to their inherent mobility; furthermore, the plate therein is not taught to be imageable by marking techniques such as pen, pencil or typewriter.
The only plates presently commercially available for such imaging techniques are conventional lithographic plates, which again require the complex ink-water balance in the printing operation. Besides the complexity in printing operation using conventional lithographic plates, such plates are costly to produce because they of necessity must require wet strength for durability on the press.
It has now been discovered that certain compositions hereinafter defined, which contain fluorinated aliphatic radicals, are capable of providing the requisite abhesiveness to driographic inks when functioning on a printing press, can be directly imaged by conventional direct-image techniques, yet will not blind during press operation.